The big picture: Variation in animal reproduction exists
- Mating between single male and female is boring
- species can reproduce without fertilization
- individual of species can change sex
- species can have both male and female sex organs
- some populations have only a few that mate
- Two modes of reproduction in animal kingdom
- Sexual:
- Asexual:
- Animals exhibit cycles of reproductive activity
- Mammalian reproduction is governed by hormones


Asexual reproduction in the animal kingdom
- Budding:
- found among invertebrates
- Fission:
- about the same size
- found among invertebrates
- Fragmentation:
- accompanied by regeneration of lost body parts
- sponges, worms, starfish
- Parthenogenesis:
- found among invertebrates and vertebrates

Review video on budding, fragmentation (+ unnecessary extras)
Parthenogenesis: Male drone bees are fertile and haploid!

Animal sex blurs the lines of male and female
- Sexual reproduction commonly between male and female
- but finding a partner may be difficult
- Stationary/slow animals can be hermaphroditic
- individual have male and female reproductive bits
- Any 2 individuals can mate
- Sex reversal occurs in different animal phyla
- oysters are males first, then turn to female when larger
- the largest female in some coral fish turn to male

Reproductive cycles are common in the animal kingdom
- Cycles controlled by hormones and environmental cues
- occur with asexual or sexual modes
- often related to seasons - ?WHY?
- Ovulation: release of eggs at midpoint of female cycle
- cycles are variable in length, synced with seasons
- sheep: cycle + pregnancy = birth in spring
- Daphnia: cycles between asexual and sexual
- seasonally related to environment
- asexual when environments are stable….

The “Handicap” of sexual reproduction

How sperm and egg come together…
- Fertilization = Fusion of haploid gametes
- Moist habitat always required for external fertilization

How sperm and egg come together…
- Fertilization = Fusion of haploid gametes
- Pheromones: chemicals used to influence physiology and behavior
- function as mate attractants
- volatiles can be detected over long distances
- pheromone production in humans is controversial

Pheromones in humans?


Internal vs External: Offspring survival
- Internal fertilization produces fewer gametes
- survival of embryos higher
- Internal associated with protection mechanisms
- parental care of young
- shells, amniotic eggs, marsupials
- Parental care not just in vertebrates..
- External fertilization produces more offspring with lower survival rates

Making and delivering gametes
- Animals usually have gonads that produce gametes
- often established early in embryo development
- Many animals also have accessory organs
- structures to carry, store, protect and nourish gametes
- e.g. fruit fly (spermathecae stores sperm in female)
- Mating may occur with more than 1 male
- males have mechanisms to prevent other male success

Mammalian reproduction governed by hormones
- Hormones coordinated across many glands/organs
- hypothalamus, pituitary and gonads
- endocrine system
- Gonadotropin-releasing hormone (GnRH) is secreted by the hypothalamus
- directs release of FSH (follicle-stimulating hormone)
- directs release of LH (luteinizing hormone)
- both from pituitary gland
- FSH and LH act on male and female gonads
- stimulate sex hormone production

Mammalian reproduction governed by hormones
- Gonads then produce and secrete 3 hormones
- testosterone, estrogen and progesterone
- found in male/females in different amounts
- Embryos: develop reproductive structures
- Maturing mammals: induce sex characteristics
- physical/behavior differences (male/female)
- Mature mammals: play role in gamete formation and reproductive cycles

Hormonal control of male system (negative feedbacks)

Most female mammals have an ovarian cycle
- Some females have linked menstrual cycle
- 10 primates, elephant shrew, some bats, spiny mouse
- Ovarian cycle:
- series of changes in ovaries for maturation and release of eggs
- Menstrual cycle: prepares uterus for pregnancy
- endometrium thickens with blood vessels
- preparation for embryo implantation
- if embryo does not implant, endometrium is shed
- Both cycles occur concurrently using same series of hormones

